Currently I'm seeing the following a lot in my logs, I'm using Sitecore 8.2 rev 2 with azure. The issue only started recently when I added some new indexes to the site for a new microsite. Any ideas of where to start investigating, I've raised with Sitecore too?
ManagedPoolThread #17 22:03:10 ERROR Exception
Exception: System.Reflection.TargetInvocationException
Message: Exception has been thrown by the target of an invocation.
Source: mscorlib
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Sitecore.Reflection.ReflectionUtil.InvokeMethod(MethodInfo method, Object[] parameters, Object obj)
at Sitecore.Jobs.JobRunner.RunMethod(JobArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain)
at Sitecore.Jobs.Job.ThreadEntry(Object state)
Nested Exception
Exception: System.AggregateException
Message: One or more errors occurred.
Source: mscorlib
at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
at System.Threading.Tasks.Parallel.ForWorker[TLocal](Int32 fromInclusive, Int32 toExclusive, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFinally)
at System.Threading.Tasks.Parallel.ForEachWorker[TSource,TLocal](IEnumerable`1 source, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally)
at System.Threading.Tasks.Parallel.ForEach[TSource](IEnumerable`1 source, ParallelOptions parallelOptions, Action`2 body)
at Sitecore.ContentSearch.AbstractSearchIndex.PerformUpdate(IEnumerable`1 indexableInfo, IndexingOptions indexingOptions)
Nested Exception
Exception: System.InvalidOperationException
Message: Sequence contains no elements
Source: System.Core
at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
at Sitecore.ContentSearch.Azure.CloudSearchUpdateContext.Delete(IIndexableId id)
at Sitecore.ContentSearch.SitecoreItemCrawler.Update(IProviderUpdateContext context, IIndexableUniqueId indexableUniqueId, IndexEntryOperationContext operationContext, IndexingOptions indexingOptions)
at Sitecore.ContentSearch.AbstractSearchIndex.<>c__DisplayClass93_2.<PerformUpdate>b__0(IndexableInfo info, ParallelLoopState parallelLoopState)
at System.Threading.Tasks.Parallel.<>c__DisplayClass17_0`1.<ForWorker>b__1()
at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask)
at System.Threading.Tasks.Task.<>c__DisplayClass176_0.<ExecuteSelfReplicating>b__0(Object )
Looks like there is a patch for this from Sitecore, hopefully this will resolve the issue.